[tsan] Do not report errors in __destroy_helper_block_

There is a synchronization point between the reference count of a block dropping to zero and it's destruction, which TSan does not observe. Do not report errors in the compiler-emitted block destroy method and everything called from it.

This is similar to https://reviews.llvm.org/D25857

Differential Revision: https://reviews.llvm.org/D28387

llvm-svn: 291868